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排序方式: 共有635条查询结果,搜索用时 31 毫秒
51.
Jayapalan Kasthuri Jayadevan Santhanalakshmi Nagappan Rajendiran 《Transition Metal Chemistry》2008,33(7):899-905
The oxidative coupling of phenols with 4-aminoantipyrine (AmNH2) has been studied by UV–visible spectroscopy using platinum nanoparticles as catalyst. The rate of antipyrilquinoneimine
dye formation depends on the nature of substrates, temperature, pH, and the use of microheterogeneous media such as sodium
dodecylsulphate (SDS), cetyl trimethylammonium bromide (CTAB) and Triton X-100 (TX-100). The reactivity trend observed for
differently substituted phenols follows the order: 3,5-dimethylphenol > phenol > o-chlorophenol > o-nitrophenol. The rate of dye formation is greater at acid pH than at basic pH and the optimum pH is 5.4. A reaction pathway
is proposed, involving the activation of o-chlorophenol with AmNH2 by metal nanoparticles and concomitant reactions of free radicals. Transmission electron microscopy results show that the
particle size is 20 nm for the platinum nanoparticles involved in catalysis.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
52.
53.
Mahesh S. Majik Perunninakulath S. Parameswaran Santosh G. Tilve 《Helvetica chimica acta》2008,91(8):1500-1504
A straightforward synthesis of (S)‐pyrrolam A is described. The synthesis involves in situ generation of the phosphorane 3 , followed by an intramolecular Wittig reaction to furnish (S)‐pyrrolam A. 相似文献
54.
Subhash P. Chavan Mahesh Thakkar Ashok B. Pathak Mohan M. Bhadbhade 《Tetrahedron》2005,61(15):3873-3879
The first enantiospecific synthesis of (+)-β-herbertenol, from naturally occurring R-(+)-citronellal, employing Taber's diazo decomposition protocol as the key step, is described. 相似文献
55.
4S-Aminoproline polypeptide 2 forms unusual β-structure in trifluoroethanol that switches to the polyproline II (PPII) form in aqueous medium, while 4R-aminoproline peptide 1 retains PPII form in both solvents. This first instance of a polyproline derivative showing a β-structure is attributed to competitive pH-dependent (4-NH(3)(+)/NH(2)) stereoelectronic effect (4R vs 4S) and the overriding importance of stereospecific intra/intermolecular H-bonding in (2,4)-cis-4S-aminoproline in contrast to (2,4)-trans-4R-aminoproline oligomers. 相似文献
56.
Mahesh Chander Gupta 《Accreditation and quality assurance》2010,15(10):591-593
The ISO/IEC 17025 standard requires that all documents that form part of the management system of the organization must be
controlled. However, as customary, the certificates issued from testing or calibration laboratories do no bear any unique
identity mark/number similar to other documents to announce control over the document. This leaves enough room for doubt to
many in treating this document at par with other management system documentation. Some auditors had raised this question during
accreditation visits. 相似文献
57.
Mahesh Kumar Thirumaleshwara N. Bhat Mohana K. Rajpalke Basanta Roul Neeraj Sinha A.T. Kalghatgi S.B. Krupanidhi 《Surface science》2011,605(15-16):L33-L37
InN layers were directly grown on Ge substrate by plasma-assisted molecular beam epitaxy (PAMBE). The valence band offset (VBO) of wurtzite InN/Ge heterojunction is determined by X-ray photoemission spectroscopy (XPS). The valence band of Ge is found to be 0.18 ± 0.04 eV above that of InN and a type-II heterojunction with a conduction band offset (CBO) of ~ 0.16 eV is found. The accurate determination of the VBO and CBO is important for the design of InN/Ge based electronic devices. 相似文献
58.
Mahesh Kumar Mohana K. RajpalkeBasanta Roul Thirumaleshwara N. BhatNeeraj Sinha A.T. KalghatgiS.B. Krupanidhi 《Applied Surface Science》2011,257(6):2107-2110
Ultra thin films of pure silicon nitride were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma with a high content of nitrogen atoms. The effect of annealing of silicon nitride surface was investigated with core-level photoelectron spectroscopy. The Si 2p photoelectron spectra reveals a characteristic series of components for the Si species, not only in stoichiometric Si3N4 (Si4+) but also in the intermediate nitridation states with one (Si1+) or three (Si3+) nitrogen nearest neighbors. The Si 2p core-level shifts for the Si1+, Si3+, and Si4+ components are determined to be 0.64, 2.20, and 3.05 eV, respectively. In annealed sample it has been observed that the Si4+ component in the Si 2p spectra is significantly improved, which clearly indicates the crystalline nature of silicon nitride. The high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM) and photoluminescence (PL) studies showed a significant improvement of the crystalline qualities and enhancement of the optical properties of GaN grown on the stoichiometric Si3N4 by molecular beam epitaxy (MBE). 相似文献
59.
Mahesh Kumar Basanta Roul Thirumaleshwara N. Bhat Mohana K. Rajpalke Neeraj Sinha A. T. Kalghatgi S. B. Krupanidhi 《Journal of nanoparticle research》2011,13(3):1281-1287
One of the scientific challenges of growing InN quantum dots (QDs), using Molecular beam epitaxy (MBE), is to understand the
fundamental processes that control the morphology and distribution of QDs. A systematic manipulation of the morphology, optical
emission, and structural properties of InN/Si (111) QDs is demonstrated by changing the growth kinetics parameters such as
flux rate and growth time. Due to the large lattice mismatch, between InN and Si (~8%), the dots formed from the Strannski–Krastanow
(S–K) growth mode are dislocated. Despite the variations in strain (residual) and the shape, both the dot size and pair separation
distribution show the scaling behavior. We observed that the distribution of dot sizes, for samples grown under varying conditions,
follow the scaling function. 相似文献
60.
Recent advances in the synthesis of C-5-substituted analogs of 3,4-dihydropyrimidin-2-ones: A review
3,4-Dihydropyrimidin-2-ones act as a versatile scaffold in organic synthesis, which serves as a significant template for the development of various therapeutic agents and shows a wide spectrum of activities. The attractive application of 3,4-dihydropyrimidin-2-ones in organic synthesis is undoubtedly owing to C-5 ester group, which is responsible for the change in its bioactivity. Introduction of various groups like electron-withdrawing and electron-donating groups at positions 1, 2, 3, 5, and 6 greatly increased biological activity. Significant efforts have been undertaken to exploit different synthetic routes to synthesize various derivatives of 3,4-dihydropyrimidin-2-ones. This review article gives a comprehensive account of the synthetic utility of C-5 substitution of 3,4-dihydropyrimidin-2-ones used in the design and synthesis of different types of compounds with greater emphasis on recent literature. 相似文献